The subject invention relates to a heavy vehicle transmission auxiliary gear box including a power cylinder where a piston is constructed of non-metallic materials and is prevented from becoming misaligned during operation. The invention also relates to a method of assembling the piston where the non-metallic piston is not damaged during assembly.
Heavy vehicles generally utilize transmissions to achieve selected speeds between an engine and an output shaft. A typical transmission includes a main gear box and an auxiliary gear box. The main gear box may include five gear ranges that may be selected by a vehicle operator. The auxiliary gear box may include a splitter gear box, a range gear box, or both.
The auxiliary gear box of the typical multi-speed transmission may be actuated automatically based upon system conditions or may be actuated by an operator switch. An auxiliary gear box gear change is typically driven by a power cylinder. The power cylinder includes a piston driven by a fluid, such as air. The fluid actuates the piston and drives a collar to select a particular output from the auxiliary gear box. The collar engages gears.
Conventionally, the piston is manufactured from metallic materials such as steel. It would be desirable to have freedom in the selection of materials, other than metallic materials, used to manufacture the piston. However, such alternative materials often require additional structural support to prevent the piston from becoming misaligned or improperly seated. That is, the piston may lean or tilt within the piston cylinder. When the piston is improperly seated, the piston is unable to effectively drive the collar to engage the gears and select the particular output from the auxiliary gear box.
It would be desirable to efficiently mount and retain the piston to prevent the piston from leaning or tilting within the piston cylinder so that the piston may be constructed of alternative, non-metallic materials and will still properly drive the collar to engage the auxiliary gear box.
In a disclosed embodiment, a piston is constructed of a non-metallic material. The piston is also properly supported so the piston does not become misaligned during operation or damaged during assembly. A transmission assembly includes a power cylinder and an auxiliary gear box. The transmission assembly also includes a multi-speed transmission main gear box. A piston housing is associated with the auxiliary gear box. A piston shaft is further included in the transmission assembly. The shaft includes proximate and distal ends and an abutment element. The abutment element extends outwardly from the proximate end of the shaft. A piston is assembled in the transmission assembly by mounting the piston on the proximate end of the shaft.
After mounting the piston on the shaft, a retaining device is secured on the proximate end of the shaft for retaining the piston on the shaft against the abutment element. As a result, less rigid, non-metallic materials may be used to construct the piston. Such materials typically tend to lean and tilt within the piston housing. However, in the subject invention, pistons constructed of these materials are firmly retained on the shaft against the abutment element. Also, the proximate end of the shaft includes a step portion. The step portion of the shaft facilitates efficient assembly as the retaining device can be quickly assembled to the shaft by securing the retaining device to abut the step portion of the shaft. As such, the non-metallic piston is not damaged during assembly.
Accordingly, the subject invention provides a piston constructed of less rigid, non-metallic materials where the piston is properly supported by the retaining device and the abutment element such that misalignment of the piston is avoided. Further, the subject invention provides a method of efficiently assembling the non-metallic piston in the transmission assembly by incorporating a step portion that avoids damage to the piston during assembly.